Digital electronic signal implementation has spurred technology changes within the telecommunications field as well as changes in sensitive electronic instrumentation. As clock-speed in digital circuitry increases, so do the problems in maintaining signal integrity such as controlling mutual cross-talk or reflection (impedance mismatch) between signal carrying conductors.
There also has been a desire to miniaturize electronic devices and to increase the number of discrete functions performed by a single device. These latter desires have resulted in more electronic functions being performed within a smaller cabinet volume, specifically within a limited surface space on a printed circuit board (PCB). This has lead to more signal interaction and thus greater disruption between neighboring components within the confined space, or the multi-functional devices themselves may be influenced by neighboring equipment.
Older connector designs were based on the flow of low frequency signals (around 50 Hz) using relatively high voltage and high current levels. Contemporary digital signals operate at high frequency (approaching 1 GHz) with signal amplitude on the order of microvolts. With such high speed, low voltage signals, transmission can occur from the "outer skin" of a conductor. In such cases, the impedance characteristics of the interconnect is important.
New multi-function connectors mounted on a PCB and limited to a defined cabinet space are subject to the problems associated with the technology advances described above. Shielded connectors that allow circuitry to attain characteristics allowing for the propagation of high-speed signals, have set the pace for connector designers and manufacturers.
In response to the forces of digital signal implementation and miniaturization, connector designers have paid particular attention to the telecommunications problem of crosstalk. One design limitation has been the shielding for the electronic signal element (and connector terminal path). Ideally, the signal element needs to be enclosed by an equally-spaced air gap (the best possible dielectric) in the form of an annulus bounded by a metal shield. There has been a gradual drift toward using coaxially-shielded components for placement on a PCB or in other equipment.
Optimal coaxial shielding is achieved by a circular cross-section connector (or cylindrical longitudinal inter-connect) with virtually no cross-sectional change over its length. As such, the distance between the center of the connector (where the signal resides) and the shielding is preferably uniform over the length of the connector with no constriction in flow of signal. Usually these types of connectors are relatively expensive machine-turned connectors.
Most connectors, however, use stamped components that are easy and cost-effective to manufacture. Typically, in such stamped structures, the internal contact terminals are rectangularly shaped and thereby deviate from the ideal annular structure. Shielding such contacts requires an equally-spaced dielectric resulting in a rectangular shield structure. There is also a deviation from the ideal circular cross-section because of the diagonal distance from the signal conductor to the shield at a corner. This non-ideal shielding is referred to as pseudo-coaxial. In most connector applications, because of the rectilinear contact pitch requirements, shielding is of the pseudo-coaxial type. It is, therefore, desirable to provide shielding for a pseudo-coaxial connector that simulates the ideal coaxial environment as closely as possible.
One problem in pseudo-coaxial connector design is that changes in cross-section within the uniformly-extending outer casing cause impedance changes, resulting in reflection loss of the signal. It is, therefore, also desirable to provide a connector that avoids such impedance changes in the connection from PCB to PCB or from PCB to component.
Right angle or horizontal (straight) connectors such as Metral.TM. connector receptacles, manufactured by FCI/Berg Electronics Group, Inc. of Valley Green, Pa., are commonly utilized for many telecommunication backplane applications. Backplane connectors are generally designed to have a high density multi-pin input/output structure to interconnect a telecommunications backplane to a daughter card.
Therefore, a need still exists for a right angle or straight connector having shielding between rows and columns that addresses all of the above-described problems with prior connectors, thereby providing a pseudo-coaxial connector design that simulates the ideal coaxial structure. There also is a need for a shielded connector that is relatively inexpensive to manufacture.